In recent years, an environmental protection issue has attracted much attention and it is strongly required to save electricity more than before as part of the environmental protection. Further, for example, the development of various electronic apparatuses each including a function of measuring actual power consumption on each occasion is strongly required in order to display the present power consumption amount for calling the user's attention to power saving and control the operation of suppressing the power consumption amount less than a preset amount.
For example, a large-scale computer such as a server includes a power supply unit mounted thereon and is operated as a computer system by supplying electric power from the power supply unit to a main board.
With the above computer system, a power measurement circuit that measures input power (that is, actual power consumption) of the power supply unit must be incorporated in the power supply unit in order to monitor actual power consumption on each occasion.
However, most of the power supply units do not include the power measurement circuit and it is impossible to know actual power consumption of the whole system in a computer system configured on a computer including a power supply unit mounted thereon that includes no power measurement circuit.